Evaluation of best management practices to reduce nutrient contaminant losses in runoff from broiler litter-amended soils. I. Alum additions

Abstract

The effect of alum [Al₂(SO₄)_3*14H₂O] on reducing phosphorus (P) concentrations in runoff water from broiler litter-amended soils was evaluated in various simulated rainfall events. Additions of alum at a 20% (w/w) rate caused a significant reduction in the "soluble" (CaCl₂-extractable) P fraction of the broiler litter matrix. As a result, the soluble P fraction added to the soils through litter application was 43% and 75% less for the 6 t/ha and the 20 t/ha litter treatments with alum than for their untreated (0 alum) counterparts. Total phosphorus (TP) concentrations in runoff for the 6 t/ha and 20 t/ha treatments with no alum were highly enriched, averaging 2.59 mg/L and 6.10 mg/L, respectively. At the highest litter rate (i.e., 20 t/ha) the 20% alum treatment achieved a 52% reduction in the concentration of TP in runoff as compared to that of the no-alum treatment. However, the impact of alum was more notable in reducing dissolved P (DP) losses. Average DP concentration losses for the 20 t/ha broiler litter rate (no alum) was 3.55 mg/L, a value significantly higher than the 1.0 mg/L threshold that has been suggested as a potential limit to control runoff P losses from agricultural fields. At said broiler litter application rate the 10% and 20% alum treatments resulted in reductions of 58% and 70% of the DP concentrations in runoff, respectively. The observed DP concentration losses from the litter treatments containing 20% alum met the 1 mg/L threshold value in practically all instances. Total P losses in runoff were positively correlated with both the amount of CaCI2-extractable P applied to the soils and soil P levels (Olsen) during different stages of the simulation events. The nutritional contents (N, P, and K) of the Bermuda grass samples were reflective of the broiler litter rate. Higher nutritional contents were generally observed with the 20 t/ha treatments as compared to those at the 6 t/ha rate with no alum, even though the effects were statistically significant only for nitrogen. Alum did not seem to exert a significant impact on nutritional content of the Bermuda grass, although a slight decrease (non significant) in both N and P was observed at the 20% alum rate for the 20 t/ha broiler litter rate.